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Total and Free Carnitine

Does this test have other names?

Quantitative plasma carnitine, plasma carnitine, plasma acylcarnitine analysis

What is this test?

This test measures the amount of a substance called carnitine in your blood. It looks at how much usable or "free" carnitine you have. It compares that with the total amount in your body.

Carnitine is a compound that's present in nearly every part of your body. Your cells normally use the fats in your body for energy. Without carnitine, your body has trouble digesting fatty acids. It can't turn fats into energy. It uses the sugar in your blood for energy instead.

Some people have a carnitine deficiency. If your body can't use carnitine, you have low blood sugar and can become weak, tired, and anemic. You may have heart and kidney problems. Some people even get progressive muscle diseases like muscular dystrophy.

About 1 in every 100,000 babies born in the U.S. has a carnitine deficiency. Newborns are usually screened for a condition called primary carnitine deficiency. Some people also get a carnitine deficiency because of type 2 diabetes, cancer, heart problems, or kidney problems. This problem is more common in Japan. In that country 1 in every 40,000 babies is born with a primary carnitine deficiency.

Getting tested helps your healthcare provider find out whether you are able to use carnitine as you should.

Why do I need this test?

Your healthcare provider may order this test if you are being treated for type 2 diabetes, cancer, an enlarged heart, or kidney disease. In some cases, these conditions can affect how you use carnitine.

This test is often given to babies shortly after birth. It is also given to toddlers, especially if they show signs of carnitine deficiency. These signs include eating problems, vomiting, confusion, seizures, and muscle weakness.

What other tests might I have along with this test?

If your healthcare provider thinks you have another disease or inherited disorder, you may need other tests. These include:

  • Complete blood count. This test looks for blood disorders such as anemia.

  • Serum electrolytes. This looks for an imbalance of sodium, potassium, or other electrolytes in your blood.

  • Blood sugar (glucose). This measures your blood sugar and helps diagnose diabetes.

  • Tests to look for liver injury and disease

  • Blood gas. This looks for an acid-base imbalance in your blood.

  • Urine tests. These check your urine for signs of a kidney infection, urinary tract damage, infection, or diabetes.

Your healthcare provider may also talk to you about genetic testing if he or she think there is a genetic reason you can't absorb carnitine.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Test results are a percentage of the amount of free carnitine compared with the total amount of carnitine in your blood. A ratio greater than 0.4 suggests you have a carnitine deficiency. Also if your total serum carnitine is less than 40 micromoles per liter (μmol/L), you may have a carnitine deficiency.

Results also depend on your physical condition and age.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

What you eat may affect the results of this test.

How do I get ready for this test?

Ask your healthcare provider whether you should not eat or drink anything but water before this test. Also be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 


Medical Reviewers:

  • Sather, Rita, RN
  • Snyder, Mandy, APRN